KR20010101135A - Wireless base station system, and wireless transmission method - Google Patents

Abstract

Transmit diversity is achieved using the diversity antennas 11a and 11b between the radio base station apparatus 10 and the communication terminal apparatus 20 only in a communication channel (packet) or a control channel directed to a specific user (FACH or AICH). It also executes transmission adaptive array antenna control.

Description

Wireless base station apparatus and wireless transmission method {WIRELESS BASE STATION SYSTEM, AND WIRELESS TRANSMISSION METHOD}

In mobile communication, fading causes significant deterioration in the quality of a received signal. There is a diversity technique as an effective countermeasure against such fading. In this diversity technology, transmission with high communication quality is usually realized by using a plurality of received signals. For example, if the two antennas of the receiver were far enough apart, the fading fluctuations are each independent. Therefore, the probability that the power of the signals received by the two antennas is reduced at the same time is reduced. Diversity technology uses this principle to prevent the low power of the received signal on the receiver side.

However, there are various limitations in realizing diversity in a communication terminal apparatus such as a mobile station. Therefore, in order to realize diversity at the transmitter side of the base station, which is to be realized at the receiver side of the mobile station, the transmission diversity technique is examined.

As shown in Fig. 1, the transmit diversity transmits a signal having the same phase toward the mobile station 3 from the antennas 2a and 2b of the base station 1, and the antenna having a high level of the received signal in the mobile station 3 is shown. To select. According to this transmission diversity, fading can be suppressed to improve communication quality.

In transmission diversity, however, fading can be suppressed to improve communication quality. However, the effect of suppressing interference to other stations and the interference imparting suppression effect cannot be exhibited. In particular, in the CDMA system, the interference suppression effect is important because, in particular, by suppressing interference to other stations, efficient communication can be performed individually and system capacity can be increased.

Disclosure of the Invention

SUMMARY OF THE INVENTION An object of the present invention is to provide a radio base station apparatus and a radio transmission method capable of suppressing fading to improve communication quality and also reducing interference transmission power per mobile station by suppressing interference imparting to other stations.

MEANS TO SOLVE THE PROBLEM The present inventor pays attention to the transmission adaptive array antenna (smart antenna) technique which exhibits the interference suppression effect, The communication channel (including a packet) to which this transmission adaptive array antenna technique can be applied, or a control channel toward a specific user is provided. Only in (forward access channel (FACH) or acquisition indication channel (AICH)), a radio base station apparatus and a radio transmission method that combines transmission diversity antenna technology with transmission diversity to exhibit both a fading suppression effect and an interference suppression effect. Realized.

That is, the main point of the present invention, as shown in Fig. 2, is the radio base station apparatus 10 and the communication terminal apparatus 20 only in a communication channel (including a packet) or a control channel (FACH or AICH) directed to a specific user. Transmit diversity is performed using the diversity antennas 11a and 11b, and transmit adaptive array antenna control is performed.

The present invention relates to a radio base station apparatus and a radio transmission method in a digital radio communication system, and more particularly, to a radio base station apparatus and a radio transmission method in a direct sequence-code division multiple access (DS-CDMA) scheme.

1 is a conceptual diagram for explaining transmission diversity;

2 is a conceptual diagram illustrating a wireless transmission method of the present invention;

3 is a block diagram showing a configuration of a radio base station apparatus according to Embodiment 1 of the present invention;

4 is a block diagram showing part of the configuration of the radio base station apparatus according to the second embodiment of the present invention.

Best Mode for Carrying Out the Invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(Example 1)

There are two transmission diversity schemes: closed loop transmission diversity and open loop mode transmission diversity. In the present embodiment, the case of the closed loop mode transmission diversity will be described. The present invention can also be applied to a case of a frequency division duplex (FDD) scheme or a time division duplex (TDD) scheme. Here, the case of the FDD method will be described. In addition, the case where the radio transmission method of the present invention is applied only to a communication channel (including a packet) and a control channel directed to a specific user (FACH or AICH) will be described.

3 is a block diagram showing the configuration of the radio base station apparatus according to the first embodiment of the present invention. This radio base station apparatus is arranged a space apart from the space diversity possible, and has a processing system having two diversity antennas 101 and corresponding receivers 103 and transmitters 104 provided for each diversity antenna 101. It is equipped with two. In addition, switching between transmission and reception in each receiver and transmitter is performed by the common devices Dup 102a to 102c. In the case of the TDD system, the switching of the transmission and reception in each receiver and transmitter is performed by a changeover switch instead of a shared device.

In the actual communication, since a plurality of channels are multiplexed, a separation section for separating received signals for each channel is provided at the receiver side at the receiver side, and at the transmitter side, the multiplexed channel transmission signals are multiplexed at the front end of the transmission RF circuit. Although multiple parts are provided, in order to simplify the description, one channel is described in FIG. 3, and the description of the separation part and the multiple part is omitted.

The signal transmitted from the communication terminal apparatus is received by the diversity antenna 101 composed of a plurality of (three in FIG. 3) antenna elements 101a to 101c, and passes through the receivers Dup 102a to 102c, respectively. To the receive RF circuits 1031a to 1031c of the 103. In the reception RF circuits 1031a to 1031c, predetermined radio reception processing (down conversion, A / D conversion, etc.) is performed on the reception signal. In the actual communication, the received signal subjected to the radio reception process is separated into individual channels.

The received signal subjected to the radio reception processing is transmitted to matching filters (MF) 1032a to 1032c, respectively, and despread using the spreading code used at the time of spreading modulation on the transmission data on the communication terminal device side. In this manner, the despread signal is transmitted to the reception adaptive array antenna AAA (coming direction estimation) circuit 1033, respectively.

The reception AAA circuit (or the arrival direction estimation circuit) 1033 performs the reception AAA process or the arrival direction estimation process. These processes will be described later. The signal on which these processes are performed is transmitted to the combining circuit 105 for each diversity antenna, synthesized by the combining circuit 105, and obtained as a received signal. The weight information obtained by this receiving AAA process or the direction of arrival estimation and the angle information regarding the direction of arrival are transmitted to the transmission weight calculation circuit 1042 of the transmitter 104.

On the other hand, the transmission signal is transmitted to the modulation circuit 106 and digitally modulated. The signal after modulation is transmitted to the spreading modulation circuit 107 and spread-modulated using a predetermined spreading code. At this time, the spreading code uses the same in two processing systems. The signal (transmission signal) after spreading modulation is transmitted to the transmission weight multiplier 1043 via the transmission diversity circuit 1041 of each transmitter 104. The transmit diversity circuit 1041 performs transmit diversity processing in accordance with the transmit diversity control signals 1 and 2.

The transmission weight multiplier 1043 multiplies the transmission weight calculated by the transmission weight calculation circuit 1042 to the transmission signal by the respective multipliers 1043a to 1043c provided corresponding to the antenna. The transmission signal multiplied by the transmission weight is transmitted to the transmission RF circuits 1044a to 1044c, respectively, for predetermined radio transmission processing (D / A conversion, up-conversion, etc.). At this time, control signals for transmission power control by the closed loop and / or open loop method are input to the transmission RF circuits 1044a to 1044c, and the transmission power is controlled in accordance with the transmission power control signal. In actual communication, transmission power control is performed on a transmission signal multiplied by transmission weight, and then transmission signals of a plurality of channels are multiplexed. Radio transmission processing is performed on this multiplexed signal. The transmission signal subjected to the radio transmission is transmitted from the respective antenna elements 101a to 101c toward the communication terminal device via the common devices 102a to 102c.

Next, the operation of the radio base station apparatus having the above configuration will be described.

The signal received from the diversity antenna 101 is wirelessly received by the receiving RF circuits 1031a through 1031c for each antenna element 101a through 101c, and then despread by the matching filters 1032a through 1032c to receive the receiving AAA circuit (or To a direction estimation circuit 1033.

In the receiving AAA circuit (or the direction of arrival estimation circuit) 1033, a weight or direction of arrival for forming an appropriate reception directivity pattern is obtained using the uplink signal received by each antenna element. This weight information and arrival direction information (arrival angle) are transmitted to the transmission weight calculation circuit 1042, so that the transmission weight is calculated. There are various methods for calculating the transmission weight by obtaining the reception directivity weight and the direction of arrival information from the received signal.

The first method is a method in which the reception AAA circuit (or the arrival direction estimation circuit) 1033 obtains the reception weight in the reception AAA process, and calculates the transmission weight using this weight. For example, the method of obtaining reception weight by beam steering is mentioned. In addition, IEICE TRANS. COMMUN., VOL. E77-B. NO. 5 MAY 1994 "Spectral Efficiency Improvement by Base Station Antenna Pattern Control for Land Mobile Cellular Systems". Include this here.

In this method, since the frequencies used for transmission and reception are different in the FDD scheme as shown in Fig. 3, if the weights obtained by the reception AAA processing are used as they are for the calculation of the transmission weights, they become different directional patterns at the time of transmission. . For this reason, the weight of the weight is regenerated by using the weight received by the transmission weight calculation circuit 1042 in the reception AAA process. The regeneration method of this weight is described in the IEICE TRANS. COMMUN., VOL. E77-B. NO. 5 MAY 1994 "Spectral Efficiency Improvement by Base Station Antenna Pattern Control for Land Mobile Cellular Systems". This is also included here.

In this method, in the case of the TDD scheme, since the frequencies used for transmission and reception are the same, the transmission weight calculation circuit 1042 calculates the transmission weight using the weights obtained by the reception AAA processing as they are.

The second method obtains the reception weight in the reception AAA process in the reception AAA circuit (or the arrival direction estimation circuit) 1033, estimates the arrival direction of the uplink signal from this reception weight, and transmits the transmission weight from this estimated value. It is a method of calculating. In the receiving AAA process, since the pressing direction is set by the pressing steering, the arrival direction is not necessarily determined. Therefore, the direction of arrival is estimated from the candidate of the direction of arrival by detecting the beam direction at which the desired wave power is maximized using the reception weight obtained by the reception AAA process.

In this way, after estimating the direction of arrival, the estimated value (angle information) is transmitted to the transmission weight calculation circuit 1042, so that the transmission weight is calculated to face the beam according to the estimated value. As a method for calculating the transmission weight from the obtained estimated value, a table in which the estimated value and the transmission weight are associated with each other is prepared in advance, and after obtaining the estimated value, a method of obtaining the transmission weight with reference to the table or beamforming using the obtained estimated value is adaptively performed. The method of obtaining a transmission weight is mentioned.

The third method is a method of estimating the direction of arrival of the uplink signal without using the reception weight and calculating the transmission weight from this estimated value. Here, the method of estimating the direction of arrival of the uplink signal is not particularly limited. For example, any one of those described in "Design and Analysis Method Workshop (10th)-Adaptive Signal Processing Technique with Array Antenna and Introductory Course for High Resolution Arrival Wave Estimation in Antenna and Radio Waves-October 30, 1997". Use the method.

In this way, after estimating the direction of arrival, the estimated value (angle information) is transmitted to the transmission weight calculation circuit 1042, and the transmission weight is calculated to face the beam in accordance with the estimated value. As a method of calculating the transmission weight from the obtained estimated value, similarly to the second method, a table in which the estimated value and the transmission weight are associated is prepared in advance, and after obtaining the estimated value, a method of obtaining the transmission weight with reference to the table or forming the beam using the obtained estimated value A method of adaptively obtaining a transmission weight may be given.

On the other hand, the transmission signal is digitally modulated by the modulation circuit 106, and then spread-modulated by the spreading modulation circuit 107 using a predetermined spreading code (same spreading code for two diversity antennas), and is transmitted. The data is transmitted to the multipliers 1043a to 1043c of the transmission weight multiplier 1043 via the diversity circuit 1041.

The transmit diversity circuit 1041 executes transmit diversity in accordance with the transmit diversity control signals 1 and 2. Specifically, in the transmission diversity circuit 1041, the weights of the transmission diversity control signals 1 and 2 are multiplied by the transmission signal after spread modulation.

The weights of the transmission diversity control signals 1 and 2 are phase offsets or closed offsets of phases and powers in the closed loop mode. This closed loop mode includes a mode using a phase offset as a transmit diversity control signal and a mode using a phase offset and a power offset as a transmit diversity control signal. In the present embodiment, any of the closed loop modes can be applied similarly to the case where the phase offset is used as the transmit diversity control signal or the phase offset and power offset are used as the transmission diversity control signal.

In the closed loop mode, phase rotation (for example, 90 °) is performed on one side of the antenna (here, a diversity antenna composed of a plurality of antenna elements) with respect to one antenna (here, a diversity antenna composed of a plurality of antenna elements). Transmission) and a power offset (for example, a power ratio of 8: 2 or inverse 2: 8) are added. Control regarding the offset is determined at the communication terminal device side. In other words, it is determined from the signals transmitted from both antennas to the communication terminal apparatus how much phase difference, phase difference and power difference should be added to the signal, and the control information is transmitted to the radio base station apparatus. Transmission is performed in accordance with the control information.

The transmission signal given the offset by the transmission diversity circuit 1041 is multiplied by the transmission weight in the multipliers 1043a to 1043c of the transmission weight multiplier 1043. This transmission weight is calculated by the transmission weight calculation circuit 1042 based on the weight information and the angle information obtained by the reception AAA circuit and the arrival direction estimation circuit as described above. In this way, the transmission signals multiplied by the transmission weights are transmitted toward the communication terminal apparatus in a beam-forming state after predetermined radio transmission processing is performed in the transmission RF circuits 1044a to 1044c, respectively. In this case, parallel diversity transmission is performed from two diversity antennas 101 spaced apart by a spatial diversity possible distance.

In the non-closed loop mode, the spreading-modulated transmission signal is multiplied by the transmission weights in the multipliers 1043a to 1043c of the transmission weight multiplier 1043.

The wireless base station apparatus according to the present embodiment can suppress fading by the spatial diversity effect in the communication channel and the control channel directed to a specific user, and can exhibit an interference imparting suppression effect by narrowing the spatial directivity. Therefore, communication quality is improved by fading suppression, and communication with each communication terminal device can be performed efficiently, thereby reducing the influence on others and increasing system capacity. In addition, since the communication quality is improved, there is no need to increase the control amount in the transmission power control and there is no need to shorten the control cycle. It is also effective against shadowing due to the spatial diversity effect. Since the spatial directivity is narrowed, communication can be performed efficiently and the transmission power can be reduced.

In the configuration shown in Fig. 3, the transmission signal after the spread modulation process is multiplied by the phase offset in the closed loop mode and multiplied by the transmission weight. The multiplication of the phase offset and the transmission weight may be performed by the same processing unit together. That is, one multiplier may be configured such that the phase offset multiplication and the transmission weight multiplication can be performed on the transmission signal after the spreading modulation process. Thereby, even if the closed loop mode is applied, it is possible to cope without changing the hard scale (without increasing the multiplier).

(Example 2)

In the present embodiment, a case of applying to STTD (Space Time Transmit Diversity) which is an example of an open loop mode will be described. Also in this case, the present invention can be applied to the frequency division duplex (FDD) system and the time division duplex (TDD) system. In addition, the case where the radio transmission method of the present invention is applied only to a communication channel (including a packet) and a control channel directed to a specific user (FACH or AICH) will be described.

4 is a block diagram showing part of the configuration of the radio base station apparatus according to the second embodiment of the present invention. In FIG. 4, the same code | symbol as FIG. 3 is attached | subjected about the same part as FIG. 3, and the detailed description is abbreviate | omitted.

The transmitter side of the radio base station apparatus includes a modulation circuit 106 for digitally modulating a transmission signal, a transmission diversity circuit 201 for performing transmission diversity processing on the modulated transmission signal, and a transmission diversity processing transmission signal. A spreading modulation circuit 202 for spreading modulation processing, a transmission weighting multiplier 1043 for multiplying the transmission weight calculated by the transmission weighting calculation circuit 1042 to a transmission signal after spreading modulation, and a transmission in which the transmission weight is multiplied. There are transmission RF circuits 1044a to 1044c that perform predetermined wireless transmission processing on the signal.

Next, the operation of the radio base station apparatus having the above configuration will be described.

The operation until the reception weight information or the arrival direction information is acquired using the uplink signal from the communication terminal device, and the transmission weight is calculated from the reception weight or the arrival direction information acquired by the transmission weight calculation circuit 1042 is performed. Same as Example 1.

On the other hand, the transmission signal is transmitted to the modulation circuit 106 and digitally modulated. The digitally modulated signal is transmitted to the transmit diversity circuit 201. In the transmit diversity circuit 201, a transmit diversity operation (STTD encoding) is performed on a digitally modulated transmit signal. In STTD encoding, a calculation is performed to obtain (-S2 *, S1 *) as a signal to be transmitted at the same time from another transmission antenna for each two consecutive symbols S1 and S2. "*" Represents a complex conjugate.

The transmit diversity calculated transmit signal is transmitted to the spread modulation circuit 202. In the spreading modulation circuit 202, spreading modulation processing is performed on a transmission signal using a predetermined spreading code (same spreading code for two diversity antennas).

The spread modulated transmission signal is multiplied by the transmission weights in the multipliers 1043a to 1043c of the transmission weight multiplier 1043. As described in the first embodiment, this transmission weight is calculated by the transmission weight calculation circuit 1042 based on the weight information and the angle information obtained by the receiving AAA circuit or the direction of arrival estimation circuit. In this way, the transmission signal multiplied by the transmission weight is transmitted toward the communication terminal apparatus in a beam-forming state after the predetermined radio transmission processing is performed by the transmission RF circuits 1044a to 1044c, respectively. In this case, parallel diversity transmission is performed from two diversity antennas 101 spaced apart from each other by space diversity.

The radio base station apparatus according to the present embodiment can suppress fading by the spatial diversity effect in the communication channel and the control channel directed to a specific user, and can also exhibit the interference imparting suppression effect by narrowing the spatial directivity. Therefore, the fading suppression improves the communication quality and enables efficient communication with each communication terminal device, thereby reducing the influence on others and increasing system capacity. In addition, since the communication quality is improved, there is no need to increase the control amount in the transmission power control and there is no need to shorten the control cycle. It is also effective against shadowing due to the spatial diversity effect. Since the spatial directivity is narrowed, efficient communication can be performed and transmission power can be reduced.

Further, in the open loop mode, it is not necessary to transmit a control signal from the communication terminal device to the radio base station device, so that control between the communication terminal device and the radio base station device can be simplified.

The present invention is not limited to the above embodiments, and various modifications can be made. For example, in the first and second embodiments, the case where the adaptive array antenna reception is performed by the receiver of the radio base station apparatus is described. However, the present invention can be similarly applied to the case where the receiver does not perform the adaptive array antenna reception. In the first and second embodiments, the case where transmission and reception of the uplink and the downlink are performed by the FDD method is described. However, the present invention is similarly applied when the transmission and reception of the uplink and the downlink are performed by the TDD method. can do.

The wireless base station apparatus of the present invention calculates a transmission weight from two diversity antennas composed of a plurality of antenna elements arranged at intervals by a distance capable of spatial diversity, and a reception weight obtained from an uplink signal or an angle in a direction of arrival. And a multiplier for multiplying the transmission weight by a transmission modulated transmission signal by using a predetermined spreading code and employing a transmitter provided for each of the two diversity antennas.

According to this configuration, fading can be suppressed by the spatial diversity effect in the communication channel and the control channel directed to a specific user, and an interference suppression effect can be exerted by narrowing the spatial directivity. Therefore, the fading suppression improves the communication quality and enables efficient communication with each communication terminal device, thereby reducing the influence on others and increasing system capacity. In addition, since the communication quality is improved, there is no need to increase the control amount in the transmission power control and there is no need to shorten the control cycle. It is also effective against shadowing due to the spatial diversity effect. Since the spatial directivity is narrowed, communication can be performed efficiently and the transmission power can be reduced.

The radio base station apparatus of the present invention adopts a configuration including offset providing means for giving a phase offset or a phase offset and a power offset to the transmission signal in the above configuration.

According to this configuration, even in the closed loop mode, fading can be suppressed by the spatial diversity effect in the communication channel and the control channel directed to a specific user, and an interference suppression effect can be exhibited by narrowing the spatial directivity. .

In the above-described configuration, the radio base station apparatus of the present invention adopts a configuration in which the multiplication unit serves as the offset providing unit.

According to this configuration, even if the closed loop mode is applied as the transmission diversity, it is possible to cope without changing the hard scale (without increasing the multiplier).

The radio base station apparatus of the present invention adopts a configuration including an arithmetic unit in which the transmitter performs a transmit diversity operation on a transmission signal before spreading modulation processing.

According to this configuration, the fading can be suppressed by the spatial diversity effect in the communication channel and the control channel directed to a specific user by the transmit diversity in the open loop mode, and the suppression of interference due to the narrowing of the spatial directivity It can be effective.

The communication terminal apparatus of the present invention is characterized by performing wireless communication with the radio base station apparatus. As a result, fading can be suppressed due to the spatial diversity effect in the communication channel, and the interference imparting suppression effect can be exhibited due to the narrowing of the spatial directivity, whereby more efficient wireless communication can be performed.

The wireless transmission method of the present invention comprises the steps of calculating a transmission weight from a reception weight obtained from an uplink signal or an angle in the direction of arrival, and a feedback mode in a feedback mode for a transmission signal subjected to spread modulation using a predetermined spreading code. A plurality of antenna elements arranged at intervals of a phase offset giving step, multiplying the transmission weights by the transmission signal given the phase offset, and transmission signals multiplying the transmission weights by a distance capable of spatial diversity And transmitting from two configured diversity antennas.

According to this method, in the closed loop mode, in the communication channel and the control channel directed to a specific user, fading can be suppressed by the spatial diversity effect, and an interference suppression effect can be exerted by narrowing the spatial directivity. have.

The wireless transmission method of the present invention includes a step of calculating a transmission weight from a reception weight or direction of arrival information obtained using an uplink signal, a step of performing a transmission diversity operation on the transmission signal, and a transmission signal of the transmission diversity operation. A process of performing a spreading modulation process using a predetermined spreading code, multiplying the transmission weights to a spread-modulated transmission signal, and arranging the transmission signals multiplying the transmission weights by a distance capable of spatial diversity And transmitting from two diversity antennas composed of a plurality of antenna elements.

According to this method, in the open loop mode, fading can be suppressed by the spatial diversity effect in the communication channel and the control channel directed to a specific user, and the interference suppression effect can be exerted by narrowing the spatial directivity. have.

As described above, according to the present invention, fading can be suppressed by the spatial diversity effect in the communication channel and the control channel directed to a specific user, and the interference imparting suppression effect can be exerted by narrowing the spatial directivity.

This specification is based on Japanese Patent Application No. 11-287896 of October 8, 1999. All of this is included here.

The present invention can be applied to a wireless base station apparatus and a wireless transmission method used in digital wireless communication systems, in particular, DS-CDMA.

Claims (7)

Two diversity antennas composed of a plurality of antenna elements spaced by a distance capable of spatial diversity; Calculating means for calculating a transmission weight from the reception weight or the direction information obtained using the uplink signal; A multiplication means for multiplying the transmission weight by a transmission signal subjected to spread modulation by using a predetermined spreading code, And a transmitter provided for each of the two diversity antennas. Wireless base station device. The method of claim 1, And said transmitter comprises offset providing means for imparting a phase offset, or a phase offset and a power offset to a transmission signal. The method of claim 2, And said multiplication means also serves as said offset providing means. The method of claim 1, And the transmitter comprises computing means for performing a transmit diversity operation on a transmission signal before spreading modulation processing. A communication terminal device performing wireless communication with a wireless base station device, The wireless base station apparatus Two diversity antennas composed of a plurality of antenna elements spaced by a distance capable of spatial diversity; Calculating means for calculating a transmission weight from the reception weight or the direction of arrival information obtained using the uplink signal; A multiplication means for multiplying the transmission weight by a transmission signal subjected to spread modulation by using a predetermined spreading code, And a transmitter provided for each of the two diversity antennas. Communication terminal device. Calculating a transmission weight from a reception weight obtained from an uplink signal or an angle in a direction of arrival; Giving a phase offset, or a phase offset and a power offset to a transmission signal subjected to spread modulation using a predetermined spreading code; Multiplying the transmission weights by the transmission signal given the offset; Transmitting a transmission signal multiplied by the transmission weight from two diversity antennas composed of a plurality of antenna elements spaced by a distance capable of spatial diversity Wireless transmission method comprising a. Calculating a transmission weight from a reception weight obtained from an uplink signal or an angle in a direction of arrival; Performing a transmit diversity operation on the transmitted signal; Performing a spreading modulation process by using a predetermined spreading code on the transmission signal on which the transmit diversity operation has been performed; Multiplying the transmission weights by a spread-modulated transmission signal; Transmitting a transmission signal multiplied by the transmission weight from two diversity antennas composed of a plurality of antenna elements spaced by a distance capable of spatial diversity Wireless transmission method comprising a.